A recent survey of 1,700 civil servants by the independent think tank Re:State found 76% of respondents thought it did not do a good job of tackling poor performers.

An ex-senior civil servant told the BBC that much of the Civil Service is culturally averse to performance management.

"Whitehall's known for ages it has to be less risk averse. Shrinking the Civil Service and the adoption of artificial intelligence technology make that more vital," they said.

"But don't underestimate the fear factor: fear of drawn-out grievances and fear of being accused of wasting taxpayers' money if the Civil Service was to do what big private sector firms do, which is cut to get rid of poor performers by offering some money and a settlement agreement."

A Defra spokesperson said: "Kashim Chowdhury abused the trust placed in him as a public servant and defrauded taxpayers out of almost £285,000. He will now rightly face the consequences for his actions.

"This conviction is the result of a thorough and painstaking investigation led by the Defra Counter Fraud and Investigations team. It sends a clear message that fraud against the public purse will not be tolerated and those responsible will be held to account."

The spokesperson said Defra would use "all available avenues to recover the proceeds of Chowdhury's offending on behalf of taxpayers".

Chowdhury's case also illustrates a wider issue.

He was engaged in what is being called "polygamous working", where people hold down several jobs secretly. Websites have even been set up offering people advice on how to keep their employers in the dark.

Its rise has been blamed on larger numbers of people working from home.

The government's National Fraud Initiative has identified 23 cases of "polygamous working" across London in its most recent report. It uncovered £500,000 of overpaid salaries over a period of a few months.

Alongside the fraud case, Chowdhury is involved in a legal dispute with his three siblings, who accuse him of ''bullying'' their mother into signing over half of her £2.1m home to him in the final days of her life. He denies it.

At times during his criminal trial, Chowdhury appeared confused by what he was hearing and blamed trauma for the web of lies he had spun. The jury took seven hours to reach their verdict and decided he was motivated by personal gain - stealing tens of thousands of pounds from the taxpayer.

Chowdhury now faces a significant custodial sentence.